1. Field of the Invention
The invention relates to a sensor for detecting multi-component states of stress and strain in solid materials, which is introduced into a bore made into the material and can there measure the elastic deformations caused by the surrounding stress states. The invention can be used in inter alia the building and construction industry, where, for the purpose of optimum structural maintenance and monitoring, it is necessary to check the loading in individual segments by means of accurate, long-term measurements.
2. Description of Related Art
The state of the art includes
a) the measurement of plane stress states in solid bodies, which is carried out by direct application of strain gages to the material. Owing to the chemical sensitivity of the adhesion between material and gage, this device can be used for only a limited time. Moreover, the direct application of strain gages can be brought about only by means of costly pretreatment in a construction environment owing to the need for an extremely clean condition of the application location.
b) individual strain gages which are glued on a stainless steel plate and welded onto a structure. With this arrangement, introduction into the structure is not possible. Only plane stress states can be measured. Measurements may be incorrect on account of effects of the welding process and the dependence of the welding spots on external conditions.
c) the measurement of forces by a sensor which, in the form of an overdimensioned ring with a fine outer knurling, is pressed into a bore. It is characteristic of this type of sensor that the measuring range is limited by the requirement for slip-free force transmission over the entire contact periphery. The limit is set by a material-dependent finite contact-pressure force and the friction coefficient. In practice, a strain limit of less than 0.02% is stated for the measuring range. Experience shows that this strain limit is continually exceeded at those points in structures which are of interest for monitoring. The sensor requires great precision of the bore with regard to tolerances and must be pressed in extremely accurately. This type of sensor is therefore used only in applications with low load limits, such as level measurements. Furthermore, the range may have only the low strain values mentioned above. In order to ensure this, a prior analysis of the stress states is necessary, so that no measuring errors are caused by different components.
Development of a sensor which makes possible reproducible detection of the stress states over the entire elastic deformation range of typical construction materials, in particular steel, concrete and stone. Widening the measuring range to include all the elastic strain values occurring in the construction sector is essential in highly utilized structures of an efficient structural design. It is to make possible structural monitoring which detects defects at an early stage and in this state still allows cost-effective structural maintenance countermeasures.
According to the invention, this object is achieved by virtue of the fact that
a) a strain transmission body, referred to here as the inner part 2, which is conical in the longitudinal configuration is secured in a similarly conical deformation body, referred to here as the outer part 1, by a retaining force,
b) the outer part 1 is slotted several times in the axial direction alternately from the front side and rear side,
c) the outer part 1 is at least triangular in form and thus touches the bore of the test object only with axial line-like contact ridges
d) and the inner part 2 is equipped with measuring pick-ups 3.